Treatment of metals



Patented Dec. 7, 1943 TREATMENT OF METALS Wilfred James Clifford and Henry Hewai'd Adams, Brentford, England, assignors to Parker Rust-Proof Company tion of Michigan Detroit, Mich, a corpora- No prawing. Application December 13, 1941, Se-

l'lal No. 422,875. 'In Great Britain February 4,

1938 3 Claims.

This invention relates to the treatment of metals, especially iron or steel, for instance to the treatment of metals with phosphate coating solutions in order to improve the resistance of the metals to corrosion or to provide a corrosionresisting base for paints. This application is a continuation in part of application, Serial No. 254,238, filed February 2, 1939, issued September 15, 1942, as Patent No. 2,295,545.

It is an object of the invention to accelerate the action of reagents which attack a metal surface.

It is a further object of the invention to accelerate the action of phosphate coating solutions such as zinc and manganese, l. e. to reduce the time taken by the coatingsolution to form a complete coating, or to reduce the temperature,

pecially phosphate coating solutions, can be ac-' celerated by incorporating therein a trichloromethyl group.

Asillustrative of the compounds which may be employed to provide the trichloromethyl group, we have chloral and trichloroacetic acid and the like.

The optimum concentration of the acceleratins compound in the reagent attacking the metal surface difiers with different compounds but in the case of phosphate coating solutions is in general from about .01% to .4% by weight of the solution. The proper amount of accelerator for best results may be easily determined in any case by starting the solution 011 with a small amount of the accelerator and increasing the amount added to the phosphate coating solution until the desired acceleration is obtained.

The optimum concentrations, under the conditions used, of various compounds which may be employed according to the invention are given in the following table, the results being arrived at by adding the compound to a solution of zinc dihydrogen phosphate having a normality of 11/20 free acid (determined by titrating with-the aid of methyl orange indicator) and N/5 total acid (determined bytitrating with the aid of phenolphtbalein indicator) and treating a cleaned steel sheet for two minutes at 80 C.

The cleaned steel sheet referred to here and in the examples given below is a steel sheet in its original'brlght rolled conditionrendered substantially free from grease by wiping with clean white spirit.

Optimum Substance concentration ch10 Per cent 2 Trichlnr acid While compounds of the invention may be the only accelerators present in the coating bath, they may also be employed in conjunction with other accelerators, and in other acid phosphate coating solutions, for instance, metallic accelerators such as copper compounds, or oxidizing agents such as nitrates or nitrites. The presence of copper ions appears to promote heavier and darker coatings and the presence of a nitrate, such as zinc nitrate, appears to give a slight further acceleration.

If in any of the above examples 0.001% of copper (calculated as the metal) is added to the solution, for instance in the form of the nitrate or carbonate, a darker and slightly heavier coating is obtained, and the addition of zinc nitrate results in a slight further acceleration.

While the invention has been illustrated by the treatment of steel, it is also useful in the coating of other metallic surfaces, such as surfaces containing zinc and alloys thereof.

what we claim is;

l. A composition comprising an acid phosphate coating solution containing as accelerator an organic compound which contains the trichloi'ometliyl group, said compound being dissolved in the solution in an amount which acceierates the coating action or the solution.

2. A composition of matter comprising a zinc dihydrogen phosphate coating solution containing as accelerator an organic compound contain ing the tricnlorometnyl group, Sal-d compound 4. The process which comprises treating one of the group consisting of ferrous and zinciferous surfaces with a phosphate coating solution containing as accelerator an organic compound which itself contains a trichloromethyl group, said compoundlbeing. dissolved in the solution in an amountvthataaccelerates the coating action of the solution, until there is obtained .upon the metallic surface a phosphate coating bonded to: the metallic surface by chemical reaction therewith.

5. The process which comprises treating one of the group consisting of ferrous and zinciferous surfaces with a phosphate coating solution containing zinc and as accelerator an organic compound having a trichloromethyl group said compound beingdissolved in the solution in an amount that accelerates the coating action of the' solution, until there is obtained upon the metallic surface a phosphate coating bonded thereto by chemical reaction. i v

6. The process which comprises treating one of the group consisting of ferrous and zinciferous surfaces with a phosphate coating solution containing manganese and as accelerator an organic compound having a trichloromethyl group, said compound being dissolved in the solution in an A tion, until a visible protective phosphate coat- 1 ing is obtained upon the metallic surface.

8. The process which comprises treating a surface of one of the group consisting of ferrous and *zinciferous surfaces with a phosphate coating solution containing trichloracetic acid, in an amount that accelerates the coating action of the solution, until a visible protective phosphate coating is obtained upon the metallic surface.

WILFRED JAMES CLIFFORD. HENRY HEWARD ADAMS. 

